1. Field of the Invention
The present invention is directed to a valve timing control system for a marine engine, and more particularly to a sensor arrangement of a valve timing control system for a marine engine.
2. Description of Related Art
A marine drive such as an outboard motor has a marine propulsion device powered by an engine. The propulsion device typically is a propeller and is submerged when an associated watercraft rests on a body of water. The outboard motor can employ either a two-cycle engine or a four-cycle engine. Recently, however, many outboard motors have been offered with four-cycle engines because they provide better emissions control.
Typically, a four-cycle engine includes one or more intake and exhaust valves moving between an open position and a closed position. One or more camshafts can be provided to actuate the valves in a timed manner. When the intake valves are open, air is introduced into combustion chambers of the engine through the intake ports. When the exhaust valves are open, exhaust gases are discharged from the combustion chambers through the exhaust ports.
The engine can include a hydraulically operated variable valve timing (VVT) mechanism that can change opening and closing timing of the respective valves by changing an angular position of one or a plurality of camshafts. A control device such as, for example, an electronic control unit (ECU) is used to control the VVT mechanism under various control strategies. For instance, the ECU controls the VVT mechanism either to set the valve timing at a fully advanced position for relatively high engine speeds to ensure high charging efficiency and high performance of the engine, or to set the valve timing at a fully retarded position for relatively low engine speeds to ensure high combustion efficiency, fuel economy and good emission control. Otherwise, the ECU controls the VVT mechanism to set the valve timing at a position between the fully advanced position and the fully retarded position in response to a running condition of the engine. Typically, the control by the ECU is a feedback control such that the ECU gives a target valve timing and controls the VVT mechanism to bring an actual valve timing close to the target valve timing.